1. Field of the Invention
The present invention relates to a wireless communication system, and more particularly, to a method and apparatus of power increase/decrease request of a user equipment using a plurality of frequencies in a wireless communication system.
2. Discussion of the Related Art
First of all, a network structure of a universal mobile telecommunications system (UMTS) will be described with reference to FIG. 1.
FIG. 1 is a diagram illustrating a network structure of a UMTS. As illustrated in FIG. 1, the UMTS includes a user equipment (UE), a UMTS terrestrial radio access network (UTRAN), and a core network (CN). The UTRAN includes one or more radio network sub-systems (RNS), each of which includes a radio network controller (RNC) and one or more base stations (Node B) managed by the RNC. One cell exists in one base station.
Next, a structure of a radio protocol used in the UMTS will be described with reference to FIG. 2. FIG. 2 is a diagram illustrating a structure of a radio protocol used in an UMTS. Layers of the radio protocol exist in a user equipment and a UTRAN in pairs, and takes the role of data transmission. Each of the radio protocol layers will be described. A physical (PHY) layer belonging to the first layer serves to transmit data to a radio interval by using various radio transmission techniques. The PHY layer is connected with a MAC layer through a transport channel, wherein the MAC layer is located above the PHY layer. The transport channel is divided into a dedicated transport channel and a common transport channel depending on cannel sharing.
The MAC layer, an RLC layer, a packet data convergence protocol (PDCP) layer and a broadcast/multicast control (BMC) layer exist in the second layer. The MAC layer maps various logical channels into various transport channels, and performs logical channel multiplexing for mapping a plurality of logical channels into one transport channel.
The MAC layer is connected with its upper layer, i.e., the RLC layer through a logical channel, wherein the logical channel is divided into a control channel for information transmission of a control plane and a traffic channel for information transmission of a user plane depending on types of transmission information. Examples of the control channel include a common control channel (CCCH) for transmission of common control information, a dedicated control channel (DCCH) for transmission of control information to a specific user equipment, a broadcast control channel (BCCH) for reception of system information commonly applied to cells, and a paging control channel (PCCH) for reception of paging message. An example of the traffic channel includes a dedicated traffic channel (DTCH) for data transfer of the user plane to specific user equipment.
Also, the MAC layer is divided into a MAC-b sublayer, a MAC-d sublayer, a MAC-c/sh sublayer, a MAC-hs/ehs sublayer and a MAC-e/es or MAC-i/is sublayer depending on types of the transport channel. The MAC-b sublayer serves to manage a broadcast channel which is a transport channel for broadcasting of system information, the MAC-c/sh sublayer manages a forward access channel (FACH) which is a common transport channel shared with other user equipments, and the MAC-d sublayer serves to manage a dedicated channel (DCH) which is a dedicated transport channel of a specific user equipment. Also, the MAC-hs/ehs sublayer manages a high speed downlink shared channel (HS-DSCH) which is a transport channel for high-rate downlink data transmission, and the MAC-e/es or MAC-i/is sublayer manages an enhanced dedicated channel (E-DCH) which is a transport channel for high-rate uplink data transmission.
The RLC layer serves to ensure quality of service (QoS) of a radio bearer (RB) and takes the role of data transmission. The RLC layer one or two independent RLC entities per RB to ensure QoS of the RB, and provides three RLC modes, i.e., a transparent mode (TM), an unacknowledged mode (UM), and an acknowledged mode (AM) to ensure various quality of services (QoS). Also, the RLC layer serves to control data size to allow a lower layer to transmit data to a radio interval. To this end, the RLC layer performs segmentation and concatenation of data received from an upper layer.
The PDCP layer is located above the RLC layer. In order to effectively transmit data using IP packets (e.g., IPv4 or IPv6) within a radio-communication interval having a narrow bandwidth, the PDCP layer performs header compression that increases transmission efficiency of the radio-communication interval by allowing a packet header of data to transmit necessary information only. The PDCP layer mainly exists in a packet switched (PS) zone due to its header compression function. One PDCP entity exists per RB to provide an efficient header compression function for each PS service. However, if the PDCP layer exists in a circuit switched (CS) zone, it does not provide a header compression function.
In addition, the BMC layer exists above the RLC layer of the second layer, and performs scheduling of a cell broadcast message, and broadcasts the cell broadcast message to user equipments located in a specific cell.
A radio resource control (RRC) layer located on a lowest part of the third layer is defined in the control plane only and is associated with configuration, re-configuration and release of radio bearers (RBs) to be in charge of controlling parameters of the first and second layers and controlling the logical, transport and physical channels. In this case, the RB means a logical path provided by the first and second layers for data transfer between the user equipment and the UTRAN. Generally, establishing RB means that features of a radio protocol layer and channel required for a specific service are defined and their detailed parameters and action methods will be established.
Next, a dual cell high speed packet access (HSPA) will be described. The dual cell HSPA means that one user equipment transmits data by using two frequencies at the same time to increase data transmission as much as two times of the existing E-DCH transmission. Data transmission of the user equipment using two frequencies will be referred to as a dual cell E-DCH operation. Alternatively, communication between the user equipment and the base station using a plurality of frequencies or carriers will be referred to as carrier aggregation.
A method of a power increase/decrease request of a user equipment that performs a dual cell E-DCH operation according to the related art will be described. The user equipment requests the base station to increase or decrease the power by using a happy bit. If the user equipment requests the base station to increase the power, it transmits the happy bit set to unhappy. If the user equipment requests the base station to maintain the power as it is or decrease the power, it transmits the happy bit set to happy. The base station that has received the happy bit set to unhappy transmits enhanced grants to the user equipment to allow the user equipment to transmit more data. The base station that has received the happy bit set to happy transmits previous grants as they are to allow the user equipment to transmit data as much as previous data, or transmits lowered grants to the user equipment to allow the user equipment to transmit less data.
At this time, when the user equipment performs a power increase/decrease request by using the happy bit, it can transmit a transport block greater than that selected for transmission at next transmission time interval to a network. However, the user equipment notifies the network that it transmits a transport block smaller than that selected for transmission at next transmission time interval due to grant allocated from the network.
The user equipment uses an extended transport format combination indicator (E-TFCI) to identify the size of the transport block selected for transmission at next transmission time interval. Since the size of the transport block is defined for each E-TFCI, the happy bit represents whether the user equipment can select the E-TFCI that can transmit more data than those of the E-TFCI selected at next transmission time interval.
The user equipment that performs the dual cell E-DCH operation receives grants for each of a plurality of uplink frequencies from the base station, and divides its power into powers that can be used for each of the uplink frequencies by using the received grants. Then, the user equipment determines E-TFCI for transmission at next TTI by using the divided powers and the grants for each of the uplink frequencies. At this time, an idle power of each uplink frequency corresponds to a value obtained by subtracting the power required for transmission of the E-TFCI selected for transmission for each frequency at next TTI from the powers divided for the uplink frequencies.
If the user equipment can transmit data by selecting E-TFCI that allows more data transmission than E-TFCI selected for transmission at next TTI at the power divided for the first uplink frequency, it sets the happy bit of the first uplink frequency to unhappy. If the user equipment cannot transmit data by selecting E-TFCI that allows more data transmission than E-TFCI selected for transmission at next TTI at the power divided for the first uplink frequency, it sets the happy bit of the first uplink frequency to happy.
The idle power of the user equipment will be described in more detail. If the idle power of the first uplink frequency is greater than a value obtained by subtracting the power required for transmission of E-TFCI at next TTI from the power required for transmission of minimum E-TFCI that can transmit more data than those of the E-TFCI which will be transmitted at next TTI, the user equipment sets the happy bit of the first uplink frequency to unhappy. If the idle power of the first uplink frequency is smaller than a value obtained by subtracting the power required for transmission of E-TFCI at next TTI from the power required for transmission of minimum E-TFCI that can transmit more data than those of the E-TFCI which will be transmitted at next TTI, the user equipment sets the happy bit of the first uplink frequency to happy.
In other words, according to the related art, the user equipment sets the happy bit to the idle power for each frequency. In this case, although more data can be transmitted through a specific one frequency by using the remaining power of the user equipment, a problem occurs in that more data cannot be transmitted by using the idle power for each frequency of the user equipment. Accordingly, despite that the network can allocate more data and the user equipment can transmit more data, as the user equipment does not request the network to increase the power, a problem occurs in that scheduling is inefficient.
As described above, according to the related art, as the user equipment that performs the dual cell E-DCH operation sets the happy bit with the idle power for each frequency, a problem occurs in that scheduling is inefficient.